This experiment is designed to further evaluate the function and activity of the hippocampus, which has been and continues to be a long standing goal of this laboratory. In particular, this experiment will analyze electrophysiological changes that occur within the hippocampus as subjects acquire either a hippocampally dependent or independent task, i.e. the classically conditioned 500ms and 300ms (respectively) trace eyeblink paradigms. Units with particular firing preferences to each of the two paradigms are expected. These units are also expected to be present in clusters within the hippocampus. Subsequently, to further analyze hippocampal plasticity subjects will be trained to one of the two paradigms until reaching criterion, at which point their training sessions will be changed to include both paradigms. It will then be possible to record from units as the hippocampus actively switches between learning tasks. All of this is made possible by the chronically implanted microdrive electrodes that will be used because of their potential to record the same units for an extended period of time. This electrophysiological analysis of the hippocampus will provide a strong basis for further investigations into hippocampal activity and will also have the potential for generalization to human learning.